1. Field of the Invention
The present invention generally relates to mechanical locks that are primarily used for vehicle seats, and particularly relates to the type of lock in which a rod translates axially within a housing.
2. State of the Art
Mechanical locks allow parts to move relative to each other and to lock them together when necessary. Adjustable vehicle seats commonly use this type of lock for controlling seat elevation and tilt angle. They also lock the seat on horizontal rails to position the seat from a steering wheel or an accelerator or brake pedal. Examples of such locks include Porter, U.S. Pat. No. 5,150,771 (1992), "Coil Spring or Friction-Lock Mechanisms," and Stringer, U.S. Pat. No. 5,794,470 (1998), "Mechanical Seat Lock."
The Porter lock includes a housing, a rod that can slide axially through the housing, and coil springs that are fixed within the housing and extended around the rod. The springs have a normal inside diameter for gripping the rod surface and locking the rod against longitudinal movement through the housing. The springs' grip on the rod also somewhat limits the rod from rotating.
The rod's surface may be finely scored in a direction generally transverse to the rod's longitudinal axis. The springs have surfaces roughened to an extent comparable to the rod's surface. The springs' surfaces have fine transverse score lines that are generally parallel to the score lines on the rod's surface. Transverse score lines on the springs mate with score lines on the rod's surface to prevent the rod's longitudinal movement through the springs and the housing. The transverse score lines on the springs and the rod do little to prevent of the rod's rotational movement.
The Stringer mechanical lock includes a rod that can move longitudinally within an elongated, tubular housing. The housing or rod attaches to a fixed vehicle part, and the other attaches to a part that can be moved. A pair of coil locking spring within the housing are around the rod. The normal diameter of each coil spring is slightly less than the outside diameter of the rod. Thus, the springs, in their normal state, provides a tight grip on the rod. The housing limits longitudinal movement of the springs. Consequently, the springs limit the longitudinal movement of the rod. Also, the grip of the coil springs on the rod somewhat limits the rod from rotating.
The Stringer mechanical lock also includes two end bushings. Each end bushing is at an end of one coil spring. Each bushing has an axial bore to support the rod and permit it to slide through the housing. Each bushing may also have an angled surface adjacent to the locking spring. When a large axial load is applied to the rod, the rod pulls one coil spring against the bushing's angled surface. This action cants the coil spring and changes the spring's normal or natural circular shape, thereby increasing the spring's frictional force on the rod and further limiting the rod's longitudinal movement
In sum, the mechanical locks in both Porter and Stringer include coil springs that provide tight grips on their corresponding rods to limit the rods' longitudinal and rotational movements. These mechanical locks also include additional mechanisms to further limits the longitudinal movement of its rod when large loads are applied.
The prior art does not include additional structure to prevent rotational movement of the rod. Accordingly, when a sufficiently large load is applied, the rod may rotate in a direction which may cause the rod to move longitudinally in relation to the coil springs and housing. Rod rotation can decrease the maximum load for any mechanical lock.
Not all mechanical locks have cylindrical rods. Some have square or rectangular rods that translate within a mating grove in a housing. J. Zhuang, Patent Application Ser. No. 09/088,212, filed May 29, 1998, "Mechanical Lock With A Cam-Driven Locking Pawl," discloses such a lock. Those shapes limit rod rotation. However, the Zhuang lock does not use coil springs to lock the rod in the housing.
Thus, it is desirable to prevent the rod from rotating within the housing.